This has semi-happened to me, with a different twist anyways, and I'm working on getting it sorted out now so maybe this will help you.
I was never really any good with an iron until halfways through the summer last year when I spent a week with my uncle and focused a lot on it. All of a sudden I had learned some secret to hitting irons. However, afterwords, my wood play struggled, and not being that long of a hitter that obviously hurt me as much as the iron gain helped me.
This year when the season started, I once again couldn't hit an iron. I went from hybrid straight to sand wedge. I could hit the sand wedge just fine, but even moving to a 9 iron gave me troubles and I couldn't get loft, or if I did it was a low hook or slice. I don't know what the so called 'geniuses' of this board claim, but I definitely believe that there is a different iron and wood swing. I started approaching all of my iron shots like it was a sand wedge. I just swung back focusing on a very straight left arm and pretended it was a chip from 70-80 yds out (a typical distance for me to put a little oomph on the sand wedge but not swing at max speed). My irons are going up in the air and straight (for the most part, there's still plenty of improvement room just like the rest of my game) and I'm gradually increasing my swing speed, the woods are staying strong, and I've been happy with how I've played the past couple weeks.
Dunno if that can do you much good if any, but I think what I've had happen to me kind of is the same problem so maybe that can help somehow.